Adipose tissue may play a pivotal role in causing insulin resistance. Insulin is the key enzyme regulating adipose tissue lipolysis in humans, although other hormones may influence the process. The effects of insulin on adipose tissue lipolysis "in vitro" have not been well-studied. Furthermore, whether weight loss in obese subjects mitigates the abnormalities observed in adipose tissue metabolism "in vitro" is not known. The present study addresses these issues in a systematic manner.